Data storage subsystems provide a capability for storage of large amounts of data, for example, in data storage drives that are arranged in high densities in data storage enclosures. Those data storage drives are accompanied by environmental resources such as batteries, blowers, and power supplies. The various resources must be managed to operate effectively, typically employing communication separate from the data handling, and the management is typically conducted by a service processor. An example of a service processor is a SCSI enclosure service (SES) processor. Typically, a service processor reports to a data storage control system regarding the enclosure and/or components of the enclosure. Examples comprise the temperature at points in the enclosure, battery levels, whether some component has reached a critical point, such as internal temperature, etc. Multiple enclosures may be combined into a single data storage enclosure, for example, for increasing density, and the previously separate enclosures termed virtual enclosures. Service processors for the previously separate enclosures may be employed in each of the virtual enclosures with insubstantial changes to the applications of the service processors.
External communications with the data storage subsystems may be redundant, for example employing two FC-AL (Fibre Channel-Arbitrated Loop) loops connectable to each of the data storage drives, and/or to a plurality of storage controllers of the enclosure for data handling. In one example, each data storage drive comprises an “A” port and a “B” port, each of which may be connected to a different storage controller and to a different one of the FC-AL loops. The FC-AL loops may comprise switched loops, having an SBOD (switched bunch of disks) switch to address each of the nodes of the loop. As is known to those of skill in the art, a “switched” loop emulates a true serial loop.
External communications may be required both with respect to data handling, and with respect to the management of the enclosure. For example, an external data storage controller or host may need to know the present temperature status of a power supply of the enclosure to determine the extent of data handling that may be safely conducted. Hence, the service processors are also connected to the FC-AL loops.
FC-AL loops are limited in the number of allowable addresses, and a desire is to maximize the number of addresses to be employed for data handling.